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copied!<p>If I understand your concerns correctly, you're trying to prevent any class that needs to instantiate a new Car object from having to inject all those dependencies manually.</p> <p>I've used a couple patterns to do this. In languages with constructor chaining, I've specified a default constructor that injects the concrete types into another, dependency-injected constructor. I think this is a pretty standard manual DI technique.</p> <p>Another approach I've used, which allows some looser coupling, is to create a factory object that will configure the DI'ed object with the appropriate dependencies. Then I inject this factory into any object that needs to "new" up some Cars at runtime; this allows you to inject completely faked Car implementations during your tests, too.</p> <p>And there's always the setter-injection approach. The object would have reasonable defaults for its properties, which could be replaced with test-doubles as needed. I do prefer constructor-injection, though.</p> <hr> <p>Edit to show a code example:</p> <pre><code>interface ICar { float getSpeed(); } interface ICarFactory { ICar CreateCar(); } class Car : ICar { private Engine _engine; private float _currentGearRatio; public constructor(Engine engine, float gearRatio){ _engine = engine; _currentGearRatio = gearRatio; } public float getSpeed() { return return _engine.getRpm*_currentGearRatio; } } class CarFactory : ICarFactory { public ICar CreateCar() { ...inject real dependencies... } } </code></pre> <p>And then consumer classes just interact with it through the interface, completely hiding any constructors.</p> <pre><code>class CarUser { private ICarFactory _factory; public constructor(ICarFactory factory) { ... } void do_something_with_speed(){ ICar car = _factory.CreateCar(); float speed = car.getSpeed(); //...do something else... } } </code></pre>

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